1. Field of the Invention
The present invention relates generally to clearing machines for trees and brushwood and, more particularly, to a clearing machine which harvests trees and brushwood and reduces the same to chips for subsequent use.
2. Description of the Prior Art
In contemporary forestry management, a maximum yield of lumber per acre of timberland is obtained by taking steps to insure that harvestable trees of substantial size are grown as rapidly as possible. One of these steps involves the removal of adjacent smaller trees and brushwood which would otherwise compete with the larger trees for soil nutrients and moisture and slow the growth of the larger trees. Elimination of this competition can significantly increase merchantable growth per year.
In the past, competing trees and brushwood have been eliminated by the application of herbicides, or by controlled or prescribed burning. However, recent public concern over, and legislation against pollution of the environment has rendered these two methods undesirable in certain instances, if not unavailable. Herbicides and controlled burning are not as selective as mechanical cutting. In addition, overspraying of herbicides or overspreading of flames often kills some trees which would otherwise have been harvested if permitted to grow to maturity. Herbicide application, controlled burning and mechanical cutting without harvesting have been performed on undesirable trees and brush in many other areas, such as rights of way under power lines, rangeland and the like.
Brushwood and small trees which are burned amount to a totally wasted energy source. If this material could be harvested and converted into a smaller form, such as chips, it would represent a new energy source capable of providing, for example, an appreciable portion of the fuel required to fire the boilers and other equipment in paper making mills and the like. It is estimated that the brushwood and trees harvested from one acre of timberland can yield as much as fifteen tons (1200 cu. ft.) of chips, depending on the growth density. However, there are many obstacles to be overcome in the design a machine capable of doing this. In southern timberlands, for example, the earth is fairly flat but often quite soft or boggy due to a high moisture content. Ordinary wheeled vehicles supporting the heavy machinery necessary to accomplish these tasks would exert unacceptably high earth loading pressures on soil of this type, resulting in undesirable loss of maneuverability, root damage, soil compaction, disruption of the naturally occurring nutrient layers, and increased soil erosion.
One proposed solution for accomplishing some of these objectives is disclosed in Pallarri U.S. Pat. No. 3,996,980. The machine there described has a harvesting head mounted at the front of a tractor-type wheeled vehicle. The harvesting head comprises a pair of counterrotating shearing blade assemblies which cut brush and small trees in the path of the machine close to the ground as the machine moves forward. Two vertical feed rollers deliver the cut material rearwardly of the machine to a chipper, which reduces the cut material to chips. The chips may be deposited on the ground or onto a chip loading bed towed behind the tractor. One major drawback of this machine is that it is not capable of cutting and chipping trees larger than 6 inches in diameter. It is very often desirable to be able to remove larger trees, up to 12 or 15 inches in diameter, which compete with harvestable timber, but which are too small for any practical use.
Other types of machines are available which may cut and/or chip selected trees, but these must be carefully maneuvered into position to harvest these selected trees and are not capable of clearing all of the smaller brushwood in their paths as they move forward. Many of these machines deposit the cut material directly on the ground and then drag it along the ground to a chipper. The dirt which then adheres to the material tends to foul and rapidly wear the equipment, and must be washed from the chips prior to their subsequent use.
A strong need therefore exists for a nonpolluting device which is capable of clearing and cleanly chipping brushwood and trees of a size up to approximately 15 inches in diameter, where this vegetation would compete with harvestable trees of larger size.